The present application is a continuation of International Application No. PCT/SE00/01129, filed May 31, 2000, which claims priority to Swedish Application No. 9902075-2, filed Jun. 3, 1999.
1. Technical Field
The present invention relates to a method and device for abrasion determination on a surface subjected to abrasive forces. More specifically, the invention relates to a method and device for determining abrasions on a substrate having at least two distinguishable superimposed layers that covered each other. Even more particularly, the invention relates to such a method and device for assessment of the abrasive forces to which an individual is exposed upon impact against an airbag during inflation of the airbag or against interior surfaces.
2. Background Information
Contact between two surfaces causes various types of effects that may be harmful to at least the more sensitive one of the two surfaces. Examples of such effects include pressure, friction and abrasive forces.
Reference to abrasive forces herein should be understood to refer to the forces that occur when an uneven surface slides against another surface under pressure, such as sandpaper against a piece of wood. Another example is human skin sliding against rough surfaces, such as asphalt paving or coarse textiles. The furrows that the scraping or abrasion causes on the human skin may result in injuries with consequential bleeding and scarring.
Abrasive forces may be of different types. For example, the contact surface may vary in coarseness and/or be applied with varying pressure. The coarser the surfaces and/or higher pressures, the more severe the abrasions. The more severe the abrasive forces, the higher the risks of abrasion-induced injuries and, as a consequence, of scarring.
While several methods have been developed for measuring pressure-induced damages, there still exists no satisfactory method for accurately assessing the abrasive forces that arise, for example, to the human skin in situations as described above. For example, the cloth of an airbag brought into contact with a person""s skin inside the car can cause abrasion injuries. The contact surface of the airbag varies according to its stage of inflation. In other words, it is important to study the detrimental effects that an airbag may have on the human skin in order to determine any abrasive forces. By doing so, airbags that cause as little abrasion as possible upon contact with the human skin can be developed.
In one method used for determining whether two surfaces come into contact with one another in vehicle crash tests, exposed body parts, such as the arms and the face of a crash-test dummy, are covered with a coating of paint. The coating can vary from a simple coating of lipstick to a more complex solution of pigments mixed with a hardener for suitable hardness. However, the information gained from these tests is limited. With this method, it is possible to only determine whether the two surfaces have been in contact with one another or not.
Another problem with the above method occurs in spraying the pigment solution onto the crash-test dummy. By spraying on the coating, it is difficult to obtain an evenly thick coating throughout. An even coating is necessary in order to obtain a comparable indication across the entire relevant area.
German Patent Specification DE 24 48 784 A1 describes a method and device for examining the configuration of a glass slab along its outer periphery. The inspection is performed by placing the slab in a check frame. Along a comparatively narrow section of the glass slab corresponding to its outer periphery, several layers of paper having different colors are applied, one on top of the other. As the glass slab is placed inside the frame, the slab, should its shape not coincide with that of the frame, scrapes off the paper layers where the slab configuration does not agree with that of the frame. Depending on where and how much the layers are scraped off, it is possible to evaluate the configuration of the glass slab.
SU 1596228 describes a technique in which the rotating cutting tools of an earth milling machine are coated with several layers of paint in order to determine which sections of the tool are most exposed to wear. In this case, scraping off the paint occurs gradually in the same place as the cutting tools are rotated, i.e., the larger the number of rotations, the more severe the scraping effects. However, the results of this technique only indicate that a certain spot on the cutting tool has a greater exposure to more scraping or wear damage than another spot.
Japanese Patent No. 60-177243 describes a device and method for discovering irregular wear on vehicle tires. As indicated in the Abstract, part of the tire is coated with several differently colored layers of rubber. In this case the scraping-off is gradual on those places having the greatest exposure to scraping effects as the tire is rotating, i.e., the larger the number of rotations, the more severe the scraping effects. Still, the results only indicate that one spot on the tire is more exposed to scraping damage than another spot.
In view of the above, there is a need for a method that allows a more precise assessment of the severity and extent of abrasive forces, such as those which a person may be exposed to upon impact with an inflated airbag, or against other interior surfaces of a vehicle. Further, there is a need for a device for implementing the method that is as simple as possible while at the same allowing a precise assessment of the abrasion.
The present invention provides a method and device for determining the abrasion or amount thereof on a surface subjected to abrasive forces. According to the invention, at least two distinguishable superimposed layers cover each other over a base or substrate. The layers are removable by scraping. An abrasion is measured by subjecting the layer-coated substrate to abrasive forces, which is followed by reading the degree of penetration through one or more of the distinguishable layers. Each layer is calibrated to correspond to a predetermined amount of abrasive force upon penetration of the respective layer. This is accomplished by varying the adhesion to the layer or substrate underneath. Further, the abrasive force required to scrape off a certain layer decreases the further from the substrate that the layer is located.
In one embodiment, the thickness of each individual layer decreases the further from the substrate that the layer is located. As a consequence, the adhesion of the layers decreases accordingly.
In one embodiment, the method of the present invention involves reading and assessing the location of the penetration on the substrate and/or the size of the scraped off area on the respective area.
In one embodiment, the layers have different reactants and/or crystalline properties. The layers may also have different reflection coefficients. In doing so, the various layers can react differently to radiation such that the area exposed to abrasive force can be radiated in order to identify areas exposed to abrasive force of different strength and/or different colors and or different patterns.
The method according to the invention involves the steps of applying on a substrate two or more distinguishable superposed layers that cover each other. These layers may be scraped off. The measurement of abrasion is determined by exposing the substrate with the layers applied thereon to abrasive forces. This is followed by reading the degree of penetration, if any, through one or several of the different layers, and assessing the extent of the abrasive forces. Each layer is calibrated to correspond to a premeasure of abrasive force required to penetrate the respective layer, by varying the layer""s ability of adhering to the layer or substrate underneath, the calibration being such that the measure of abrasive force required to scrape off a certain layer decreases the closer to the free surface that the layer is located.
One advantage of the invention is that it offers the ability to simulate the effect of abrasive forces on complex surfaces, such as human skin, in a more precise manner.
By applying several layers that are distinguishable from one another on the substrate, it is possible to determine the strength of the abrasive force within predetermined intervals. In other words, in order to scrape off the first layer, an abrasive force of a prestrength is required. A stronger abrasive force can be required to simultaneously scrape off the next layer underneath, and so forth. The layer that becomes exposed within an area subjected to abrasive forces thus indicates the strength of the abrasive force.
In accordance with one embodiment of the invention, the thickness of the individual layers differs. For example, the closer the layer is located to the surface the thinner the layer. By so doing, the adhering force of the layers thus is reduced.
In accordance with another embodiment of the invention, not only is the strength of the penetrating abrasive force assessed, but also the place of penetration on the surface subjected to the abrasive force. As such, the invention provides a picture of the location of the abrasive forces, or where the abrasive forces are occurring.
In another embodiment of the invention, the extent or area of scraped-off sections on each respective layer is assessed. This assessment provides a picture of the extent of the abrasive forces.
In a further embodiment of the invention, both the position and the extent on the surface subjected to abrasion are determined.
It should be noted that on those spots where several layers are scraped off, this process takes place in one single scraping motion. Thus, it is not a situation involving a gradual scraping off action with one layer at a time being scraped off. Instead, the present invention is directed towards determining the instantaneous strength of the abrasive force and, in accordance with the various embodiments such as mentioned above, also the extent and/or location thereof.
In accordance with a preferred further development of the inventive method, the distinguishing feature may be visual. For example, the individual layers can be differently patterned and/or colored. This feature can also be invisible to the eye. For example, the distinguishing feature can be achieved by using different reactants to radiation (such as UV radiation) in the various layers. The reaction to the radiation varies in a measurable way so that the section subjected to abrasive forces can be radiated in order to identify the areas exposed to abrasive force of different strength. In other embodiments, the individual layers could also have different crystalline properties and/or reflection coefficients.
In accordance with another embodiment of the invention, the identification of the uncovered parts of the respective layer is preferably made by scanning the entire section digitally and thereafter data processing the section in a suitable manner. An identification method of this is described in European Patent No. 442699. In this case, the scanned object is conventionally radiated by a beam of light. The two-dimensional image information is then picked up with the aid of a sensor device. The sensor device reproduces the scanned object and converts the light image to electrical signals.
In accordance with another embodiment of the invention, the layers can be subjected to an abrasive force, for example, contact with an expanding air bag. Tests of this nature by means of a prototype of the inventive object have resulted in the pattern shown in FIG. 3, discussed hereinafter. The pattern clearly shows marks due to the airbag seams. As indicated, these seams cause more severe abrasion injuries than the smoother sections of the airbag.
In accordance with another embodiment of the invention, the layers are applied on a crash-test dummy that is subjected to a vehicle collision. The dummy, coated in accordance with the teachings of the invention, then provides information as to the potential location and extent of the abrasion to an individual in a collision. This information, together with other information such as the video recordings of the crash process, indicates which interior surfaces inside the vehicle cause abrasion injuries. In addition, it is possible to coat the interior surfaces of the vehicle with layers in accordance with the teachings of the invention, in order to obtain information as to which surfaces are hit and cause abrasion.
Advantages of the invention include being able to obtain clear information as to within which intervals the strength of the abrasive force resides. At the same time, it becomes possible to assess the location and the extent of the abrasion. Another advantage provided by the invention is that it is simple to use.
As indicated above, the invention includes a substrate onto which at least two layers that are distinguishable from each other are applied. The layers are preferably removable by scraping. The layers are applied one on top of and covering the other. Each layer is calibrated with respect to its different ability to adhere to the layer underneath or to the substrate. As such, it corresponds to a predetermined measure or strength of scraping force at which the respective layer is penetrated. The measure or strength necessary to scrape off a certain layer diminishes the closer to the free surface that the layer is located.
The invention offers the possibility to more precisely simulate complex surfaces such as human skin. This makes it possible to assess the abrasion. At the same time, the inventive device is simple to manufacture and to use.
According to one embodiment of the inventive device, the thickness of the individual layers differ. Preferably, the thickness of the layers decreases the closer to the surface that the layer is positioned. In doing so, the resistance against abrasion also differs. The variable resistance against abrasion that the individual layers possess is essential to the method and to the device in accordance with the invention. In accordance with another embodiment of the inventive device, the layers are applied a sheet made from a suitable material. A device of this kind is useful in the implementation of the method according to the invention. A sheet of a non-stretchable material is easy to apply on surface comprising a single curve whereas a sheet of a stretchable material, such as plastic foil, could be applied on surfaces comprising double curves or having a more complex configuration.
The sheets can consist of a plastic material. Preferably, the material is a plastic foil. Due to the higher pliability of the material and its stronger tendency to withstand elongation and stress, this embodiment is more suitable for surfaces comprising double curves or having a more complex configuration, such as in the face of a crash-test dummy.
An advantage of this device is that it may be manufactured under suitable and controllable conditions. This guarantees that the layers possess the desired properties and eliminates the inconvenience of having to apply the layers directly on a substrate such as a test dummy, making it possible to use presheets.
According to another embodiment of the inventive device, the individual layers may include at least one scrape off coat and one top coat, the surface of the latter layer being harder than that of the scrape-off coat. In this case, the thickness of the top coats may decrease as seen from the substrate upwards. Accordingly, weaker abrasive force are required to penetrate a topcoat located closer to the surface. It is also possible to vary the ability to adhere. The adhesion against any one underlying layer that a layer composed of a top coat and a scrape off coat possesses is determined by the adhesion between the top coat and the scrape off coat underneath, i.e., in the layer. Briefly speaking, it is the top that determines the resistance against abrasion in the type of layer.
Additional advantageous embodiments of the invention will become apparent from the following description of the invention.
It may be desirable to adapt the adhesion of the individual layers to predetermined abrasive force levels for the purpose of simulating as best possible the properties of human skin, and to easily obtain interpretable indicia of abrasion. One possibility in this regard is to use the damage codes of the ARS system (Abrasion Rating System) described in xe2x80x9cAirbag-Induced Skin Abrasions: Design Factors and Injury Mechanisms"" by Reed, Schneider and Burney, University of Michigan, 1992, set forth in the table below.
By adapting the properties of the layers as exemplified below, tests show that it is possible to relate each layer to a predetermined ARS level, thus facilitating the subsequent interpretation of the effects of abrasion.
Table 1: ARS System Levels
ARS
Level Description of damage
1) Abrasion not sufficiently severe to cause bleeding or flow of fluids 24 hours or less after the accident. Erythema or brief discoloration of skin.
2) Bleeding, dripping fluids or formation of crust at the earliest after 30 minutes but within 24 hours of the accident.
3) Superficial, incomplete abrasion lesion on the skin, characterized as lesion on the upper layer of dermis and fine spot-like bleeding from the vessels.
4) Deep, incomplete abrasion lesion characterized as lesion on the lower dermis layer with more extensive spot bleeding.
5) Complete abrasion lesion throughout the entire dermis and into the subcutaneous tissue.